Officials said Pennsylvania American Water crews shut off water while they were digging in the area. It also cut off water to the Schneider's plant, which builds up ammonia pressure, and some ammonia leaked.

Seventeen people were treated, and 11 were taken to the hospital as a precaution.

"Two individuals had respiratory complaints, the rest of them were primarily taken for further evaluation," said Todd Pritchard, chief of the Medical Response Team South. "Since they were employees, we just want to make sure they were OK."

The dairy is in a residential neighborhood, but officials say residents were never in danger.

"It is a safe scene and we can't stress enough for the local residents, you're in no immediate danger, we're not ordering any type of evacuation," said Alvin Henderson, chief of Allegheny County Emergency Services.